As an example of using the spectrometry device as a detector of a liquid chromatograph, a photodiode array absorbance detector that uses a photodiode array (PDA) as a photodetector of a spectrometer may be cited. The photodiode array absorbance detector measures the absorption spectrum of an analysis sample flowing into a flow cell by radiating light emitted by a light source on the flow cell through which effluent of the liquid chromatograph flows, and dispersing the light which has passed through the flow cell by a diffraction grating and converging the light on the photodiode array.
Normally, a lamp is used as the light source, and a light source chamber housing the lamp and, in addition, cooling means for cooling the light source chamber are provided. This is because, normally, an optimum surface temperature for realizing optimum light emission is set to the lamp used as the light source, and the light source chamber has to be cooled in such a way that the lamp surface is at this temperature. As the cooling means, a forced air cooling fan, which is inexpensive and has a high cooling efficiency, is used in many cases.
In the case of a spectrophotometer that adopts a single-beam measurement technique such as the photodiode array absorbance detector, if the ambient room temperature around the device changes, the amount of light entering the photodiode array changes due to a change in the amount of light of the light source or deformation of the spectrometer by thermal expansion, for example, and baseline noise or drift may thereby occur. Accordingly, to increase the sensitivity of the spectrophotometer, it is important to stabilize the light entering the photodiode array.
There is an example where, to suppress a change in the amount of light of the light source caused by a change in the room temperature, the number of rotations of the cooling fan is changed according to a change in the room temperature and the temperature of the light source is kept constant to thereby suppress a change in the amount of light of the light source and reduce the noise/drift (for example, see Patent Document 1).